Processing a ragged 2 dArray

Question

/*I need to store some information in a ragged 2d array. So i want this program to take in ex. 3 names, and for each name i want the array to store a number of courses for each name. ex. name anders have take 3 courses, oop, intP , appDesign.

I have tried to make it proces this information into the array with 2 for loops, but there is somthing wrong with the loops. Hope anybody can help or give me a clue. Regards

package assignment10;

import java.util.Scanner;

public class NewClass {

    public static void main(String[] args) {

        System.out.println("Enter the number of students you want to enter into the database");

        Scanner number = new Scanner(System.in);

        int numberStudents = number.nextInt();

        int[] numberOfStudents = new int[numberStudents];

        for (int i = 0; i < numberOfStudents.length; i++) {

            numberOfStudents[i] = i+1; // here i avoid the length 0

        }
            System.out.println("you have entered " + numberStudents + " number of students");
        for (int j = 0; j < numberOfStudents.length; j++) {
            System.out.println(numberOfStudents[j]);
        }

        // This is here im having trouble Where in the for loops have i made the //mistake
        String [][] nameCourseArray =new String [numberOfStudents.length][];
        Scanner name = new Scanner(System.in);
        Scanner courseName = new Scanner ( System.in);
        for( int i = 0 ; i < numberOfStudents.length; i++ ){ // maybe here
            System.out.println("enter name of student");
            nameCourseArray[0][0] = name.nextLine();
            for( int j = 0;j < nameCourseArray[0].length; j++){ // or here
                System.out.println("Enter the courseName");
                nameCourseArray [i][j] =courseName.nextLine();


            }        


    }

}
}

`String [][] nameCourseArray =new String [numberOfStudents.length][];` the second dimension has no length — Zion, Apr 17 '15 at 11:57
do not use a two dimensional array. Create a Class student that contains an array with all completed courses. — RaphMclee, Apr 17 '15 at 12:02

score 1 · Accepted Answer · answered Apr 17 '15 at 11:57

You only initialize the first dimension of the array :

String [][] nameCourseArray =new String [numberOfStudents.length][];

This means nameCourseArray[i] is null, so nameCourseArray[0][0] and nameCourseArray[i][j] would throw a NullPointerException.

You must initialize the i'th sub-array with :

nameCourseArray[i] = new String[someLength];

Processing a ragged 2 dArray

1 Answers1